Radio interference eliminator



y 20, 1941- s. F. THUNBERG 2,242,333

RADIO INTERFERENCE ELIMINATOR Filed Oct. 3. 1939 Tijl- :2 IO JO 5! Q 26 25 Z! n j f yENTO Y ffigz Y Patented May 1941 Thlnberplolmingasweden,

erdimnd allgnortollootrolucorporaflombovu,nol.,

Application October's, ms, was 201,641

ino ommarm BClaims. (Cl. m-sc) My invention relates to means for eliminating radio interference caused by an electric motor. More especially, my invention relates to such .means incorporated in an electrically operated vacuum cleaner.

In accordance with my invention the electric motor is surrounded by at least two metallic shields which are electrically insulated from each other. A pair of condenser circuits are bridged across the armature of the motor, either at the brushes, or at the motor terminals. The midpoint of one circuit is electrically connected by means of a direct metallic connection to one of the shields, while the midpoint of the other circuit is electrically connected in similar manner to the other shield. The inner of the two shields is preferably the metal housing of the motor itself, while the outer shield is a metal case surrounding the motor housing. In addition, there is preferably provided a casing around the aforesaid case and electrically insulated therefrom and from the motor, its purpose being to prevent the operator from accidentally contacting any of the charged parts. This casing may be the outer' casing of the vacuum cleaner itself.

Further objects and advantages of my invention will be apparent from the following description considered in connection with the accompanying drawing, which forms a part of this specification, and of which:

Fig. 1 is a cross-sectional view of a portion of a vacuum cleaner em odying my invention;

Fig. 2 is a-wiring diagram in accordance with one embodiment of my invention; and

Fig. 3 is a wiring diagram in accordance with another embodiment.

Referring more particularly to Fig. 1, reference character It indicates the exterior casing of a vacuum cleaner, which may be of any suitable material. One end of thecasing I is closed by means of an end member I I, removably securable thereto in any suitable manner.

Disposedinspaced relation withinthecasing II are transverse partitions l2 and II. Partition It is preferably made of electrical insulating material, while partition I! may be of sheet metal provided with perforations. Supported between the partitions l2 and it is ametalcase it which is insulated from the partition I! by meansofaring llofinsulatingmaterial. A ring liofinsulatingmaterialisdisposedwithin case Wand servestosupportone endofan electric motor II. The other end of the motor is supported from partition i3.

Mountedononeendofthearmatureshaftof the motor are fan rotors II, the adjacent portionofcase liservingasafanhousing- A condenser unit I2 is mounted adjacent to the end of the motor, and as shown in'Fig. 1, is con-' veniently secured to the motor housing I1. Figs. 2 and 3 show two diflerent ways in which the condensers of unit 32 may be connected in accordance with the present invention.

According to Fig. 2, a condenser means comprising a pair of condensers 2| is bridged across the terminal of the field coils, that is, across the motor leads l9 and 20 and the midpoint of the condensers is connected metallically by means of a conductor 23 with the motor housing II, which constitutes the inner of two shields. Another condenser means comprising a pair of condensers 24 is likewise bridged across the terminals of the field coils and'the midpoint is connected metallically by means of a conductor 26 with the case It. The condenserszl and 24 serve first of all to suppres the asymmetrical interference voltage. If the capacity of these condensers is not suflicient to also suppress the symmetrical interference voltage, an additional condenser 31 may be bridged acros the motor leads I! and 20.

The embodiment shown in Fig. 3 is similar to that illustrated in Fig. 2, with the exception that the circuits including the condensers 2| and 24' are bridged across the brushes of the motor instead of across the terminal of the field coils. As

described in connection with Fig. 2, the mid-v point of each circuit is electrically connected to the motor housing i1 and the case l6, respectively. Due to the fact that the case It is electrically insulated from all of the surrounding parts of the cleaner by means of the insulating ring it and the partition ll of insulating material, it is impossible for the operator to receive a shock even'should the end cap ll be removed or should he reach into the casing III from the opposite end when the dust bag ll has been removed.

As shown Fig. 1, a cylindrical member 30 is carried by e partition ll, the purpose of scope is not to be limited thereby but is to be determined by the appended claims.

What I claim is:

1. In a device of the class described, an electric motor having an armature, a metal housing around said armature, a metal case around and electrically insulated. from said housing, a first condenser means bridged across said armature and having a midpoint electrically connected to said housing by a direct metallic connection, and a second condenser means bridged across said armature and having a midpoint electrically connected to said case by a direct metallic connection.

2. In a device of the class described, an electric motor having an armature and brushes, a metal housing around said armature, a metal case around and electrically insulated from said housing, a first condenser means bridged across said brushes and having a midpoint electrically connected to said housing by a direct metallic connection, and a second condenser means bridged across said brushes and having a midpoint electrically connected to said case by a direct metallic connection.

3. In a device of the class described, an electric motor having a field, a metal housing around said field, a metal case around and electrically insulated from said housing, a first condenser means bridged across the terminals of said field and having a midpoint electrically connected to said housing by a direct metallic connection, and asecond condenser means bridged across said terminals and having a midpoint electrically connected to said case by a direct metallic connection.

4. Apparatus as claimed in claim 1 in which said metal housing constitutes the housing or the electric motor.

5. Apparatus as claimed in claim 1 including an ungrounded condenser bridged across the leads of said electric motor.

6. Apparatus as claimed in claim 2 including an ungrounded condenser bridged across the leads of said electric motor.

7. Apparatus as claimed in claim 3 including an ungrounded condenser bridged across the leads of said electric motor.

8. In a vacuum cleaner, an outer casing, a metalcase supported within and electrically insulated from said casing, an electric motor having an armature and a metal housing disposed within and electrically insulated from both said case and said casing, a first condenser means bridged across said armature and having a midpoint electrically connected to said housing by a direct metallic connection, and a second condenser means bridged across said armature and having a midpoint electrically connected to said case by a direct metallic connection.

SIGURD F. THUNBERG. I 

